1. Field of the Invention
The present invention relates generally subsea petroleum production. More specifically, the present invention relates to production riser tiebacks which connect a production riser to a high pressure wellhead housing.
2. Description of the Related Art
Tieback connectors are used to connect a production or drilling riser to a high pressure wellhead housing. The connector must be able to withstand very large forces to keep the riser sealed to the wellhead housing. This has required rather bulky connectors to withstand these forces.
One type of tieback connector connects to a grooved profile on the exterior of the high pressure wellhead housing. The tieback connector has a cylindrical housing that slides over the upper end of the wellhead housing. A cam member, piston, and a plurality of segments are carried in the housing. Applying hydraulic pressure to the piston strokes the cam member, pushing the dogs into engagement with the grooved profile. The housing of the connector has a fairly large diameter in order to accommodate the piston, cam member and dogs. Some production platforms are designed with relatively small holes or slots through which the connector must pass. This necessitates a connector with a smaller outer diameter.
A tieback connector comprises a passive lower locking system and an active upper locking system to exert a positive locking force on the connection between a production riser and a high pressure wellhead. The tieback connector is comprised of an outer housing which carries lower locking dogs, upper locking dogs and a piston. The piston is located above the lower end of the production riser and controls the movement of the outer housing. As the piston is stroked the outer housing cams the lower dogs into grooved profile in the wellhead housing. As the piston is stroked further the upper dogs exert a force onto the production riser that locks the riser to the wellhead housing.